Solid-state lighting devices have many uses in industrial applications. Ultraviolet (UV) lighting devices have become fairly common for curing of coatings, including inks, adhesives, preservatives, etc. Solid-state lighting devices typically use less power, cost less and may have easier disposal than current mercury arc lamp devices.
Solid-state lighting devices may consist of laser diodes or light-emitting diodes (LEDs) as examples. The device typically has an array or several arrays arranged to provide light with a particular profile, such as a long, thin light region, or wider and deeper light regions. The individual elements reside in arrays, a lighting device may consist of several arrays, or several arrays arranged in modules, with the lighting device having several modules.
Generally, solid-state lighting devices may receive power from a constant voltage supply. A circuit that allows for continuous adjustment of current drives the solid-state lighting elements in the device. In some instances, this circuit may include one or more field-effect transistors or other devices that act as variable resistors. A variable voltage drop exists across these devices, resulting in a varying voltage to the array of solid-state light elements. The intensity of the light output of these devices depends upon the current driving them, so any variation in the current causes variation in the light output, an undesirable characteristic.
Current approaches do not account for the power dissipation by the variable resistors. The variable resistors operate in a circuit to continuously adjust current. As the forward voltage increases, the voltage drop across the variable resistor increases, as does the power dissipation. This makes the circuit less efficient.
In addition, the power dissipation in the variable resistors generates heat. Heat management of the variable resistors may require heat sinks, or the variable resistors themselves may have to be large and bulky.